title: [Effect of ammonium ions on the uptake of L-leucine in Saccharomyces cerevisiae. Repression and inhibition of transport systems].
abstract: L-leucine entrance into Saccharomyces cerevisiae is mediated by the general amino acid permease, GAP and two transport systems, S1 and S2, kinetically characterized. S1 is a high-affinity, low-velocity transport system, operating at lower L-leucine external concentration (0.05-0.1 mM), while S2 is a low-affinity, high-velocity transport system, operating at higher L-leucine external concentration (1.0 mM). In cells grown in minimal medium containing ammonium as sole nitrogen source the values of L-leucine entrance and uptake are smaller than those in cells grown in L-proline containing medium. When GAP is repressed by ammonium, L-leucine entrance is mediate by systems S1 and S2. Both systems are inhibited by ammonium. When GAP is derepressed, in cells grown in L-proline medium, L-leucine is transported by systems S1 and GAP (lower L-leucine external concentration), and mainly by S2 (higher L-leucine external concentration). GAP is the largest system inhibited by ammonium.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
authors.forename: N
authors.initials: N
authors.lastname: Kotliar
authors.forename: C A
authors.initials: CA
authors.lastname: Stella
authors.forename: E H
authors.initials: EH
authors.lastname: Ramos
mesh_terms: D026905:Amino Acid Transport Systems; D000645:Ammonium Sulfate / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002956:Citrulline / Q000493:pharmacokinetics; D005656:Fungal Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000493:pharmacokinetics*; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; D005656:Fungal Proteins; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins; D002956:Citrulline; D011392:Proline; D007930:Leucine; D000645:Ammonium Sulfate
vernacular_title: Efecto de iones amonio sobre la entrada de L-leucina en Saccharomyces cerevisiae. Represión e inhibición de los sistemas transportadores.